I've developed a module that implements support for the syntax of
"codice fiscale", the personal identification code used by the Italian
government to uniquely identify citizen. I think it might be of
general
use, although possibly limited to Italian users, so I'd like to give
it
a somewhat official and unbiased OID, rather than one under my arc or
SysNet's.

I'm not sure what you mean by "official and unbiased OIDs". OIDs are
either properly delegated or not. Two properly OIDs are equally
official and have no bias. They are just a sequence of numbers after
all.

Now different delegators have different biases, but these biases have
no impact on the technical aspects of the protocols.

Would it qualify as general enough for OpenLDAP's OID arc, at
least while experimental?

To qualify, the question is not whether the use is "general enough".

Simply put, the OpenLDAP OID arc is for the Project's use. It's not
for the use by other enterprises.

It primarily used for early implementations of LDAP extensions in
OpenLDAP Software, such as when the standards development organization
producing the extension specification has not yet assigned OIDs for
extension elements. It's also used for extensions specific to
OpenLDAP Software and/or the OpenLDAP Project.

Generally speaking, OpenLDAP OID should only be used to identify
elements used in OpenLDAP Software and otherwise don't otherwise have
an OID.

I believe the need for a dedicated syntax (as
opposed to IA5string, printableString or so) is that its definition,
although flawed, needs to conform to quite a few restrictions, and a
syntax that allows to detect trivial errors and single out impossible
values would be definitely helpful. I need the OID in order to submit
code along with an ITS for contrib. An OID arc would be best, because
the kit consists in:

If you use a dummy OID (e.g., 1.1) in your contribution (and document
this), then the project should, if your contribution is accepted,
assign an appropriate OID upon integration.

If you want to make use of your contribution before integration, I
would suggest you assign an OID from your arc and submit using that.

Speaking with regard to this particular situation, my primary concern
would be whether your or our assignment would conflict with that of
the organization standardizing "codice fiscale". This might be a case
where we want to consider our code an "early implementation" of a yet
published standard (where use of a .666 OID is appropriate). I'm not
familiar enough with "codice fiscale" to know whether its developers
would ever assign an OID.

If it wasn't for that, I would say: just submit the contribution to
see if there were any objections to its integration and, if none,
integrate it using either your OID (if you already assigned one) or an
OpenLDAP OID (if not).